The present invention relates to a display device suitable for use on automobiles and adapted for displaying the present position of the automobile on a map.
Modern automobiles incorporate various electronic control devices such as an engine speed controller, overspeed alarm, anti-skid control and so forth, to contribute to the increased safety of driving and to save energy. This trend gives a rise to a demand for a novel system, i.e. a display device for informing the driver of the present position of the automobile.
Hitherto, there have been proposed various present position display devices. For instance, one of the present inventors has proposed in Japanese Patent Laid-open No. 13880/1970 a display device in which a display unit provided with a map and a position indicator is disposed in the vicinity of the driver's seat to display the present position of the automobile on the map. This present position display device, however, involves a problem. Namely, in this device, the desired course is beforehand marked on the map by a color pencil or the like, and the position indicator is moved along the planned course while rotating the map, in such a manner that the direction of movement of the position indicator always coincides with the direction of running of the automobile. Accordingly, it is necessary to take the trouble of attaching and detaching maps to and from the display unit by means of an adhesive tape or the like, requiring a considerable time and labor.
In this present position display device, the running distance of the automobile is calculated from a signal derived from a detector such as a rotation detector attached to a wheel, and the indicator is made to move in accordance with the calculated output to scan the reverse side of the map to move a spot of light from a light source along the marked planned course thereby to inform the driver of the present position of the automobile. This device, however, does not have capability to read and display a specific position information on a map such as position of a gas station. In addition, this device lacks the mechanism rigidity and the driving operation of the position indicator is somewhat inaccurate, although the indication is easy to observe for the driver.